Idiosyncratic hepatotoxicity occurs in a particular subgroup of the population for which the pathogenesis is unknown. Such toxicity is not predicted by either pre-clinical animal models or pre-marketing clinical trials. While inherently toxic compounds are readily identified and removed from the development pipeline, idiosyncratic compounds are put on the market, only to wreak havoc on the larger patient population. The effects of idiosyncratic compounds on the general public include varying degrees of hepatic injury, which can lead to liver failure, transplantation, and even death. Idiosyncratic hepatotoxicity arises too frequently in the population (2.7%; In Energy and Commerce, 107th Congress, Second Session ed.; FDA: Washington, D.C., 2002, pp. 1), and is therefore a major cause for concern in the pharmaceutical industry (Meadows, M., 2002, FDA Consumer Magazine 36:1).
Currently, hepatic injury due to medications is one of the most common causes of acute liver disease and jaundice (see, e.g., Hepatotoxicity Clinical Research Network). The mortality rate of hepatic idiosyncratic drug reactions is quite high, and over half of the cases of acute liver failure in the United States are due to medications exhibiting idiosyncratic hepatotoxicity. In fact, the risks of drug induced toxicity are a primary concern of the pharmaceutical industry and accentuate the need for early and reliable predictors of potential adverse events (Frank and Hargreaves. Nature Reviews/Drug Discovery. 2, 566-580 (2003)). It is therefore clear that the current pre-clinical safety assessment systems are inadequate for the complete and comprehensive evaluation of new therapeutic entities. Yet, elucidation of the mechanisms of hepatic drug injury is often difficult.
Drug-induced liver disease is typically unpredictable and rare. Most of the medications that cause acute liver injury in humans do not produce injury in experimental models, and patients exhibiting hepatotoxicity often have multiple risk factors for liver disease (see, e.g., Hepatotoxicity Clinical Research Network).
Drug-induced liver injury is also quite variable in clinical expression (see, e.g., Hepatotoxicity Clinical Research Network). Patterns of hepatotoxic injury can mimic most other forms of liver disease, including acute viral hepatitis, autoimmune liver disease, bland cholestasis, mixed cholestatic-hepatic syndromes, acute cholangitis, microvesicular steatosis with lactic acidosis, alcohol-like steatohepatitis, and venoocclusive disease. In addition, drugs that cause hepatotoxicity are often withdrawn from use, and their mechanisms of injury remain unknown.
The majority of preliminary compound screening in the pharmaceutical industry is currently conducted using in vitro cell based assays (Lin et al., Current Topics in Med. Chem. 3, 1125 (2003)). These assays typically measure cell viability and metabolism, apoptosis or rely on the measurement of general toxicity indicators that are not applicable to pre-clinical animal studies. Conversely, traditional in vivo biomarker measurements are typically not suitable for use in high throughput cell based assays (Streiner and Norman., Health Measurement Scales: A practical Guide to Their Development and Use (Oxford University Press, Oxford, 1995); Swanson., Dis. Markers. 18, 47-56 (2002)).
A common set of analytes that could be used both to predict toxicity in vitro and gauge toxic effects in vivo would therefore be of great value. A single set of reagents and standards could be used to evaluate compounds from initial screening, through testing in pre-clinical species, and potentially in clinical trials. Such universal indicators of toxicity should meet several criteria. First, they should correctly identify toxic compounds with diverse mechanisms of action, including various chemical classes/chemotypes. Second, changes in these biomarkers should be consistent, quantifiable and reflect the degree of toxic insult. Third, assays should be adaptable to high throughput technologies without becoming prohibitively expensive. Fourth, in vivo sample collection should be non or minimally invasive, i.e. urine or blood. Fifth, since there may be a need to analyze archival samples, the biomarker needs to be stable.
Despite the clinical significance of hepatic idiosyncratic injury, this form of liver injury is a relatively unstudied area of medicine. Therefore, there is a substantial need in the art to identify and characterize biomarkers useful for predicting in vivo hepatic toxicity. The inventors describe herein the identification of several idiosyncratic hepatotoxicity biomarkers that are capable of predicting the incidence of idiosyncratic hepatotoxicity for a particular compound both in vitro as well as in vivo that meets each of the five criteria described supra.